September 07, 2009

Sand contributes to the economic stimulus

As a young kid, I was blessed with six great-aunts, who lived together in two
groups of three, one group in Nottingham and the other in the East End of
London. Visiting either somewhat eccentric group was always a treat for me,
their rambling old houses filled with strange (but still memorable) aromas,
exotic Victorian decoration, and sundry mysteries (including the outside
toilets). The London group consisted of two spinsters and a widow plus cats and,
generally, a lodger priest whom I tended to avoid. I loved visiting,
particularly if my great-aunt Grace (my favourite) had made bread pudding, still
the best I have ever tasted. But a culinary mystery, and a genuine piece of
kitchen magic, was when she preserved eggs. These were still the post-war days
when eggs were precious, and, in any case, old habits die hard. The eggs were
immersed in this strange substance, which began as a viscous fluid, diluted for
the purpose. "It's waterglass, dear," my great-aunt would explain; this struck
me as being very descriptive, since it looked like liquid glass, but little did
I realise how accurate the name was.

Waterglass is sodium silicate, or, more strictly, sodium metasilicate,
Na2SiO3, a chemical that easily absorbs water, starting
off in my Great-Aunt's kitchen as a powder, and hydrating into a viscous fluid
and then a true liquid. It seems that it penetrated the shell of an egg, sealing
off the porosity and thereby preventing access by bacteria; eggs preserved this
way could be kept for months. Waterglass showed up later in my life in various
guises, including as an sealant for various leaking bits of my early cars - it
was particularly effective for a hole in the exhaust pipe, the heat of which
would solidify a patch soaked in sodium silicate into a hard seal. The irony
today is that sodium silicate is hitting the headlines not as a means of mending
your car, but of completely crippling it. As a recent USGS news item
reported:

The Nitty Gritty of Cash for Clunkers

The government-run “Cash for Clunkers” did much more than just stimulate the
economy and raise awareness of carbon emissions. It also caused demand for a
little known and little used mineral compound called sodium silicate. The
program required that buyers of clunkers immediately kill the engine of the car
— a task most efficiently done by running the engine with sodium silicate. When
a vehicle runs for a few minutes with this compound in place of engine oil, the
engine seizes, and it cannot be reused. The other parts of the vehicles,
however, can be recycled.

The "Cash for Clunkers" project has caused a massive demand for an obscure
mineral. As the Wall Street Journal reported a few days ago, under the
headline "The
Killer App for Clunkers Breathes Fresh Life into 'Liquid Glass'," the
"designated agent of death for cars" suddenly became a highly sought-after
commodity. One chemical supplier

ordered enormous supplies and purchased prime space on Google, so that his
company popped up in searches for sodium silicate. Last week, he sold 4,600
gallons of it, and the rush is continuing. "We're working 16 hour days, and
we've got friends and family helping out filling orders."

So where does all this magic, lethal, mineral come from? As the USGS reports,
"Sodium silicate, the only soluble silica compound, is made by fusing two
industrial minerals, high-purity silica sand with soda ash." Sand to the rescue
of the global economy!

"Soda ash" is sodium carbonate, the naturally occurring form of which is the
mineral natron. And so we come back to glass - "the stone that flows." The
satisfying story that Pliny the Elder tells of the origin of glass is, sadly,
apocryphal, but it's entertaining and illustrative of the process. He describes,
in his Natural History, how Phoenician traders with a cargo of natron,
perhaps from the desert lakes of the Sahara, had put in for the night on the
eastern Mediterranean coast. Unable to find adequate rocks to support their
cooking pots over the fire, they resorted to using some blocks of their cargo.
Whatever their dinner recipe was, they had unwittingly assembled the ingredients
for glass: the soda lowered the melting point of the beach sand, and out of the
fire flowed streams of translucent liquid. It's a nice fairy-tale, but with an
important point: to melt sand on its own requires temperatures in excess of
1,600°C (2,900°F), far beyond the capability of traditional wood-burning
furnaces. The melting point has to be lowered to a practicable temperature, and
this is where the natron plays its critical part in the story. Soda has a much
lower melting point than sand and acts as a flux, an additive that makes
silica sand meltable at realistically achievable temperatures.

But of course what is being made here is sodium silicate - waterglass, a
product soluble in water, which is hardly desirable in making a wine glass or a
window. To stabilize the glass, calcium in the form of powdered limestone has to
be added, and it is entirely possible that this was first discovered by accident
through using silica sand that also contained fragments of seashells. The
resulting concoction is soda-lime glass, the everyday kind of glass that has
been used for the last three thousand years.

Sodium silicate, while it is a somewhat obscure chemical, does, nevertheless,
continue to be used in a number of different ways. It's still used as an
adhesive and sealant, in treatments for timber, concrete, and water, and as a
fire protection. Perhaps its most important use today is in the manufacture of
synthetic zeolites, clever minerals that have a whole host of uses. It's also
used in Magic Rocks. Although that name hadn't been yet coined when I was a kid,
this was the other incarnation of sodium silicate that I encountered. In the
days when chemistry sets really were chemistry sets, with ingredients capable of
causing real domestic havoc and incurring real maternal wrath, one of the more
benign but common chemicals provided was waterglass. With this, and some
compounds of different metals, a "chemical garden" could be created. Put a layer
of sand at the bottom of a glass container, add waterglass dissolved in water,
and then chunks (the magic rocks) of different metal compounds, generally
nitrates or chlorides of manganese, cobalt, copper, iron, and watch your garden
grow. The metals combine with the waterglass to form insoluble metal silicates
that precipitate and grow upwards to form exotic plant-like structures. The
colour depends on the metal, just as the colour of glass depends on the metal
added. The phenomenon was discovered in the 17th century, when waterglass was
known as "oil of sand" and played a common role in alchemy. It would seem that
Sir Isaac Newton, in his experiments in the transition between alchemy and
"chymistry," created magic gardens in oil of sand, the organic appearance of the
structures confirming the old alchemical idea that metals have a kind of life
and can "vegetate".

It's sort of fun where a simple story of disabling clunker engines can get to
- my great-aunt Grace would be pleased.